1. Field of the Invention
The present invention relates generally to a semiconductor device and more particularly to a transistor in which the diffusion length of minority carriers in its emitter region is large as compared with a prior art transistor.
In our co-pending U.S. patent application, Ser. No. 427,647, filed Dec. 26, 1973, assigned to the same assignee as the present invention, there is disclosed a transistor having a region of opposite conductivity in the emitter region to that of the emitter region. The impurity concentration in the emitter region is low, hence the diffusion length of minority carriers injected from the base region to the emitter region is long as compared with the thickness of the emitter region, and the life time of the minority carriers in the emitter region is kept long. In this earlier case, some of the current components flowing through the emitter junction or the current component injected from the base region to the emitter region is decreased and, consequently, the emission efficiency from the emitter region can be enhanced.